The importance of various putative Bordetella pertussis cell adhesins which mediate the adherence of the bacteria to mammalian cells is being investigated. We have demonstrated that pertactin, a 69 kDa surface protein, can promote the adherence of Chinese hamster ovary (CHO) cells. We have also shown that another surface protein, filamentous hemagglutinin (FHA) can also independently promote the adherence of mammalian cells. To investigate the mechanism of attachment of these protein to their cell receptor, we have studied the role of the sequence Arginine-Glycine-Aspartic Acid (RGD), which is a sequence found in pertactin and FHA, in mediating cell adherence. The adherence of CHO cells to pertactin occurs via an RGD binging site on the protein. The RGD sequence does not seem to be involved in the interaction of CHO cells to FHA, a lectin-like interaction seems more likely to be the mechanism of cell interaction used by this protein. It has recently been shown that B. pertussis can invade and survive within mammalian cells. Peptides homologous to the RGD sequence from pertactin can inhibit invasion of the bacteria. The peptides derived from the sequence of FHA with RGD had no effect on invasion. Further studies are being performed to determine the role pertactin may play in the invason of mammalian cells by the bacteria.